Combustor-boiler for rankine-cycle engines

ABSTRACT

A compact combustor-boiler construction is described that during operation will emit substantially no nitrogen oxides, while burning a fuel/air mixture essentially to completion. Nested cooled porous plug burners with a common fuel/air supply chamber are flanked by inner and outer burned gas cooler units with the coolant flow paths through the burners being connected in series with a flow path through the outer and inner cooler units in sequence whereby the coolant (working fluid) is sequentially exposed to liquid heating, nucleate boiling, film boiling and, preferably, super-heating.

[ 1 COMBUSTOR-BOIILER non 3,563,211 2/1971 Hombostel, Jr. 122/250 R RANKINECYCLE ENGINES 3,563,212 2/1971 Hoagland 122/250 R Inventor: George E. Moore, Scotia, NX.

Assignee: General Electric Cempany,

Schenectady, NY.

Filed: May 15, 1972 Appl. No.: 253,182

1.1.5. Cl fill/108, 122/235, 122/238 Int. Cl. F2211 115/00, lFZZb 31/00 Field of Search 122/235, 338, 33,

References Cited UNlTED STATES PATENTS 4/1936 Synnott 122/338 X 10/1965 122/33 8/1968 Valyi 122/33 X SUPPL y Primary Examiner-Martin P. Schwadron Assistant Examiner-Allen M. Ostrager Attorney-John F. Ahern et a1.

[ 57] ABSTRACT A compact combustor-boiler construction is described that during operation will emit substantially no nitrogen oxides, while buming a fuel/air mixture essentially to completion. Nested cooled porous plug burners with a common fuel/air supply chamber are flanked by inner and outer burned gas cooler units with the coolant flow paths through the burners being connected in series with a flow path through the outer and inner cooler units in sequence whereby the coolant (working fluid) is sequentially exposed to liquid heating, nucleate boiling, film boiling and, preferably, super-heating.

1111 Claims, 5 Drawing Figures FUEL SUPPLY COM BUSTOR-BOILER FOR RANKINlE-CYCLE ENGINES BACKGROUND OF THE INVENTION Attention has become focused on the necessity for avoiding or, at least, minimizing the emission of pollutants from engines. The pollutant emissions of prime concern are carbon monoxide (CO), nitrogen oxide (NO,), hydrocarbons (or other unoxidized or partially oxidized materials derived from the fuel) and particulates (e.g. soot or organic smoke). Of these four kinds of pollutant emissions, limitation of the levels of CO and NO,. in flame products appears to be the mostdifficult problem, because of the compromises required in the operation of the combustor unit to accomplish this.

In piston engines, the piston and cylinder must perform all the essential operations on the working fluid, i.e., compression, heating (by combustion), expansion and the transfer of mechanical energy for useful work. The built-in limitations of such an overloaded system limit the latitude available for parameter trade offs to limit CO and/or NO emissions.

Gas turbine combustors, on the contrary, employ combustion systems that are relatively free from such restraints. For this reason, gas turbine combustors generally have lower emission rates, especially for CO and hydrocarbons, though such combustors produce smoke. The smoke problem appears to be susceptible of solution, however. The one really significant pollution problem is gas turbine operation has been that of NO, emission.

The art is, therefore, in particular need of a combus tor concept that will provide the flexibility of operation required to avoid the generation of hydrocarbons or particulates and to enable compromises in operation for drastically reducing the levels of CO and NO, emission from the combustor.

SUMMARY OF THE INVENTION A compact combustor-boiler for generating the working fluid for a Rankine-cycle engine is described herein. This unit provides a flexibility of operation for flame generation and control unavailable in prior 'art devices.

The combustor-boiler construction described herein comprises at least one pair of nested cooled porous plug burners having a common fuel/air supply chamber located therebetween, said pair of plug burners being flanked by at least one outwardly-disposed burned gas cooler unit and at least one inwardly disposed burned gascooler unit, the parallel coolant flow paths through said burners being connected with the series flow path through the outer and inner cooler units.

The conduct of liquid into and through the cooling circuit results in sequential exposure to liquid heating, nucleate boiling, film boiling and, preferably, superheating in order to generate the working fluid for the Rankine-cycle engine.

BRIEF DESCRIPTION OF THE DRAWING The exact nature of this invention 'as well as objects and advantages thereof will be readily apparent on consideration of the following specification relating to the annexed drawing wherein:

FIG. 1 is a schematic representation in section of a compact combustor-boiler and a Rankine-cycle engine according to the instant invention;

FIG. 2 is a section taken through the device along line 2-2;

FIG. 3 is a section taken through the device along line 3-3;

FIG. 4 is a section taken through the device along line 4-4 and FIG. 5 is a schematic representation of the sintered particle construction of the porous plug burner and cooler units employed.

DESCRIPTION OF THE PREFERRED EMBODIMENT Combustor-boiler 10 comprises four cylindrical sintered metalwalled elements ll, l2, l3 and 14 defining in combination the annular spaces l6, l7 and 18 therebetween.

The construction of each of these elements ll, l2, l3, 14 comprises a porous wall made of sintered metal particles, for example, copper shot, bronze shot, nickel shot, stainless steel shot or any structurally sound metallic shot material, which; as sintered, will be able to retain its structural integrity and form at the temperatures to which it will be subjected during operation. The temperature exposure of the pair of burners 12, 13, cooler l1 and cooler 14 will be progressively more severe, ranging about 300 F to as high as 1200' F. The illustration in FIG. 5 shows the general relationship of the sintered metal particles I9 and interconnected voids 21 permitting continuous passage of fuel/air mixture through the porous body of each of burners l2, 13 with a pressure drop of less than 1 psi for a burner body about five-eighths of an inch thick. The pressure drop will vary as a function of the velocity of the fuel/air flow. For porous plug burners about one-half inch thick, the pressure drop is about 0.03 psi/cm/sec of gas mixture flowing under a pressure of about one atmosphere. In general, to provide a structurally sound burner body in which flame propagation therethrough will be obviated, the voids should have an effective pore size smaller than about 0.5 mm;

Porous plug elements such as is shown in the drawings have been produced from oxygen-free metal particles (e.g., copper, bronze, nickel, aluminum or stainless steel) with metal cooling tubes, such as cooling tubes 22, 23, 24 and 26 embedded therein in a graphite mold by sintering the particles. Some metals require the application of a small pressure (less than about 2 psi) thereto during sintering. The size range of the particles is not critical and may range from as little as 1 micron to more than about 2 millimeters in diameter. The extent of pressure application, when required, during sintering determines the void content (and therefore, the strength) desired in the porous body being made. The most important objective of void content control is the attainment of a low flow resistance and high structural integrity of the bodyQThe arrangement of cooling tubes 22, 23, 24, 26 also provides excellent reinforcement for the porous sintered material.

In application in which weight is an important consideration (and the temperature exposure is not excessive) aluminum shot is preferred.

Because of the high temperature encountered in steam generating unit 10 during operation, seals cannot be relied upon for hermetic closure between the far ends of each of cylindrical porous plug elements 1 1, l2, l3, l4 and manifold headers 27, 28 in the way in which seals are used in the exothermic gas generator disclosed and claimed in U. S. Patent Application Ser. No. 110,392 Moore, filed Jan. 28, 1971 and assigned to the assignee of the instant invention. The gas generator in the aforementioned application is specifically designed for very cool operation and reliance is placed upon the circulation of coolant flow at velocities to accomplish this temperature control. 1n the combustorboiler unit all connections have to be made during the sintering operation (direct connection) or by the use of high temperature brazing. Also, as may be seen from the following description, the same cooling fluid is sequentially heated several times during multiple passes through the device making for hot operation of the unit. Although no outer jacket is shown on the drawing it may be preferable to enclose unit 10 in a thermally insulated jacket to duct away the hot exhaust gases and optimized heat transfer to the working fluid.

As shown, coolant conduits 22 are in flow communication at the far ends thereof with annular manifolds 29, 31; coolant conduits 23 similarly interconnect manifolds 32, 33; coolant conduits 24 interconnect annular manifolds 34, 36 and coolant conduits 26 interconnect annular manifolds 37, 38. The liquid inputs to manifolds 29 and 32 are connected in parallel and, as well, the fluid discharges from manifolds 31 and 33 are connected in parallel.

Liquid, usually demineralized water, enters preheater 39 and passes through conduit 42 for distribution to manifolds 29 and 32. Fuel (gasoline, kerosene, etc.) depending upon its nature may be vaporized in heater 43 or may be passed directly via pipe 44 to be mixed in mixing chamber 46 with air (from the air supply shown) supplied via line 47.

The annular region 17 between burners 12, 13 is divided into annular compartments 48, 49, 51 by means of annular divider plates 52, 53. Fuel/air mixture leaving mixing chamber 46 via valves 54, 56, 57 and lines 58, 58; 59, 59 and 61, 61 connected thereto may be controllably admitted to compartments 48 (via lines 58, 58'), 49 (via lines 59, 59') and 51 (via lines 61, 61') as is shown in the drawings.

This arrangement permitting the selective use of all or part of burners 12, 13 provides a significant increase in turn-down" capability.

This fuel/air mixture is, of course, combustible and as the mixture passes through the porous walls of burners l2 and 13 (radially outward for burner 12 and radially inward for burner 13) and exits therefrom, it is ignited in annular spaces 16, 18 resulting in even, stabilized flames 62, 63 (shown for operation with all of valves 54, 56, 57 open). Initially, ignition is accomplished by the igniting means 64, 66 and, once in operation, ignition is accomplished by the existing stabilized flames spread over the respective operative combustion surfaces of elements 12 and 13.

During operation, a given temperature gradient becomes established in the porous walls of each of burners 12, 13 depending upon the unburned fuel/air mixture flow velocity so that heat generated from the fuel combustion is at least in part (about 5 to 20 percent) rejected to the interior of each of burners 12,,13 where it is efflciently removed by the fluid, e.g. water, circulating through cooling tubes 22, 23, respectively. The cooled flames are non-adiabatic.

The products of combustion leave the hot gas annuli l6, 18 passing, respectively, radially outward and radially inward. The products of combustion leaving annular space 16 give up additional heat to the fluid passing through conduits 24, this fluid having been circulated thereto from manifolds 31, 33 via piping 67.

Heat from the combustion products passing radially inward from annular chamber 18 is released both to the fluid passing through conduits 26 and also to heaters 39 and 43 (optional). Fluid flow entering conduits 26 via piping 68 is the fluid discharged from manifold 34.

The high pressure superheated vapor (e.g., steam) leaving manifold 38 is conducted via valve 69 to a prime mover 71, that may be a steam engine or a steam turbine, via line 72 for the generation of shaft power by expansion therein of this high pressure vapor.

After expansion thereof in prime mover 71, the cooled working fluid passes to condenser 73, where additional heat is removed therefrom. The condensate is then pressurized and recycled by pump 74 to heater 39. Throttling of the flow of high pressure vapor leaving valve 69 occurs at the nozzles (in the case of a steam turbine) or at the valves (in the case ofa steam engine).

Starting combustor-boiler 10 is a straightforward, simple operation. The circulation of working fluid is initiated with valve 69 set to pass incoming fluid from manifold 38 to by-pass line 76. When the temperature and pressure of this fluid have reached the proper values, valve 69 is re-set to pass the fluid to line 72 and, thence, to prime mover 71. The air flow is set at some value to provide the desired gas mixture velocity together with some preselected value of fuel flow; the igniters 64, 66 are energized and the fuel regulator (valve 77) is advanced to bring the fuel input from zero continuously through the whole range of air/fuel compositions up to the desired preselected value. The whole starting procedure may easily be accomplished in about 5 seconds.

The high temperature components of Combustor/- boiler 10 (e.g., cooler elements 11, 14) will preferably be made of stainless steel shot and tubes therefor would be made of stainless steel as well. Sintering of stainless steel shot does not require the application of pressure, but does require a sintering temperature in excess of 1,300 C, preferably l,350 C. As noted hereinabove, the particle size of the shot is not critical, however, 1 mm diameter shot (smaller than 10 and larger than 20 mesh) is preferred.

Following are approximate specifications for a combustor-boiler for supplying the steam requirements of a hp (nominal) steam engine for a vehicle:

1.2 X 10' BTU/hr.

Total Combustor Heat Loading 1.5 X 10 BTU/hr.

Burner Heat Loading Total Burner Surface Area 6 ft. Rated Unbumed Gas Velocity (77F) 0.6 ftJsec. Rated Fuel/Air Equivalence Ratio 0.9 (range: 0.7 to 0.9) Approximate Overall Dimensions 18" dia. X 18" long Combustor Hot Gas Residence Time 0.015 secs. Steam Generation Rate 900 lbs/hr.

(- 1000 psi; 1000F max.) Full Load NO, Emission Rate:

- 10 ppm (equiv. to

0.04 glmile) Full Load C0 Emimion Rate: 2 grams/mile Unburned hydrocarbons and particulates: negligible H. In a unit for generating a high temperature fluid wherein means for introducing fuel to be burned in a combustion zone, means for supplying air to burn the fuel in said combustion zone and means for circulating a fluid below the surface of wall area of said combustion zone are employed in combination to heat the fluid by the burning of the fuel, the improved combination comprising: I

a. at least one pair of spaced apart burner structures, the wall of each of said burner structures being made of sintered porous metal the voids of which have an effective port size smaller than about 0.5 mm,

b. first means embedded in the wall of the first burner structure for circulating fluid therethrough,

c. second means embedded in the wall of the second burner structure for circulating fluid therethrough,

d. a first cooler unit located in juxtaposition to and spaced from a surface of said first burner structure being disposed on the opposite side of said first burner structure from said second burner structure, said first cooler unit being adapted for the circulation of fluid therethrough,

e. third means in flow communication with said first and second means for admitting fluid thereto,

f. fourth means in flow communication with said first and second means for receiving fluid therefrom and with said first cooler unit for conducting fluid thereto, a

g. a second cooler unit located in juxtaposition to and spaced from a surface of said second burner structure being disposed on the opposite side of said second burner structure from said first burner structure, said second cooler unit being adapted for the circulation of fluid therethrough,

h. fifth means in flow communication with said first cooler unit to receive fluid therefrom and with said second cooler unit for conducting fluid thereto,

. closure means affixed to the walls of each of said pair of burner structures, said closure means to gether with the walls affixed thereto defining a closed volume,

j. means in flow communication with said closed volume for supplying a flow of fuel/air mixture thereto,

k. means in communication with the space between said first burner structure and said first cooler unit for igniting fuel/air mixture released thereto through the wall of said first burner structure and 1. means in communication with the space between said second burner structure and said second cooler unit for igniting fuel/air mixture released thereto through the wall of said second burner structure whereby non-adiabatic flame combustion can be conducted in said unit so as to insure low N0, concentrations in the burned gases.

2. The improved combination of claim ll wherein the closed volume between the burner structures is subdivided into compartments and control means are provided for the fuel/air mixture supplying means for admission of the fuel/air mixture to each compartment.

3. The improved combination of claim ll wherein the burner'structures are in the form of hollow nested cylinders.

d. The improved combination of claim 3 wherein the first and second cooler units are hollow sintered porous metal cylinders, each cylinder having means embedded in the wall thereof for the circulation of fluid therethrough.

The improved combination of claim 1 wherein the second cooler unit is made of sintered stainless steel particles.

6. In a Rankine-cycle power plant comprising means for generating a high temperature, high pressure working fluid in flow communication with an engine selected from the group consisting of steam engines and steam turbines for generating mechanical power; heat exchanger means in flow communication with said engine for further cooling of the working fluid, and pumping means for receiving the further cooled working fluid, raising the pressure thereof and returning the pressurized working fluid to said means for generating high temperature, high pressure working fluid, the improved combination in which the means for generating high temperature, high pressure working fluid comprises:

a. at least one pair of spaced apart burner structures, the wall of each of said burner structures being made of sintered porous metal the voids of which have an effective pore size smaller than about 0.5

b. first means embedded in the wall of the first burner structure for circulating fluid therethrough,

c. second means embedded in the wall of the second burner structure for circulating fluid therethrough,

d. a first cooler unit located in juxtaposition to and spaced from a surface of said first burner structure being disposed on the opposite side of said first burner structure from said second burner structure, said first cooler unit being adapted for the circulation of fluid therethrough,

e. third means in flow communication with said first and second means for admitting fluid thereto,

f. fourth means in flow communication with said first and second means for receiving fluid therefrom and with said first cooler unit for conducting fluid thereto,

g. a second cooler unit located in juxtaposition to and spaced from a surface of said second burner structure being disposed on the opposite side of said second burner structure from said first burner structure, said second cooler unit being adapted for the circulation of fluid therethrough,

h. fifth means in flow communication with said first cooler unit to receive fluid therefrom and with said second cooler unit for conducting fluid thereto,

. closure means affixed to the walls of each of said pair of burner structures, said closure means together with the walls affixed thereto defining a closed volume,

j. means in flow communication with said closed volume for supplying a flow of fuel/air mixture thereto,

it. means in communication with the space between said first burner structure and said first cooler unit for igniting fuel/air mixture released thereto through the wall of said first burner structure and 1. means in communication with the space between said second burner structure and said second cooler unit for igniting fuel/air mixture released thereto through the wall of said second burner structure whereby non-adiabatic flame combustion can be conducted in said unit so as to insure low N0, concentrations in the burned gases.

sintered porous metal cylinders, each cylinder having means embedded in the wall thereof for the circulation of fluid therethrough.

10. The improved Rankine-cycle power plant of claim 6 wherein the closed volume between the burner structures is subdivided into compartments and control means are provided for the fuel/air mixture supplying means for admission of the fuel/air mixture to each compartment. 

1. In a unit for generating a high temperature fluid wherein means for introducing fuel to be burned in a combustion zone, means for supplying air to burn the fuel in said combustion zone and means for circulating a fluid below the surface of wall area of said combustion zone are employed in combination to heat the fluid by the burning of the fuel, the improved combination comprising: a. at least one pair of spaced apart burner structures, the wall of each of said burner structures being made of sintered porous metal the voids of which have an effective port size smaller than about 0.5 mm, b. first means embedded in the wall of the first burner structure for circulating fluid therethrough, c. second means embedded in the wall of the second burner structure for circulating fluid therethrough, d. a first cooler unit located in juxtaposition to and spaced from a surface of said first burner structure being disposed on the opposite side of said first burner structure from said second burner structure, saiD first cooler unit being adapted for the circulation of fluid therethrough, e. third means in flow communication with said first and second means for admitting fluid thereto, f. fourth means in flow communication with said first and second means for receiving fluid therefrom and with said first cooler unit for conducting fluid thereto, g. a second cooler unit located in juxtaposition to and spaced from a surface of said second burner structure being disposed on the opposite side of said second burner structure from said first burner structure, said second cooler unit being adapted for the circulation of fluid therethrough, h. fifth means in flow communication with said first cooler unit to receive fluid therefrom and with said second cooler unit for conducting fluid thereto, i. closure means affixed to the walls of each of said pair of burner structures, said closure means together with the walls affixed thereto defining a closed volume, j. means in flow communication with said closed volume for supplying a flow of fuel/air mixture thereto, k. means in communication with the space between said first burner structure and said first cooler unit for igniting fuel/air mixture released thereto through the wall of said first burner structure and l. means in communication with the space between said second burner structure and said second cooler unit for igniting fuel/air mixture released thereto through the wall of said second burner structure whereby non-adiabatic flame combustion can be conducted in said unit so as to insure low NOx concentrations in the burned gases.
 2. The improved combination of claim 1 wherein the closed volume between the burner structures is subdivided into compartments and control means are provided for the fuel/air mixture supplying means for admission of the fuel/air mixture to each compartment.
 3. The improved combination of claim 1 wherein the burner structures are in the form of hollow nested cylinders.
 4. The improved combination of claim 3 wherein the first and second cooler units are hollow sintered porous metal cylinders, each cylinder having means embedded in the wall thereof for the circulation of fluid therethrough.
 5. The improved combination of claim 1 wherein the second cooler unit is made of sintered stainless steel particles.
 6. In a Rankine-cycle power plant comprising means for generating a high temperature, high pressure working fluid in flow communication with an engine selected from the group consisting of steam engines and steam turbines for generating mechanical power; heat exchanger means in flow communication with said engine for further cooling of the working fluid, and pumping means for receiving the further cooled working fluid, raising the pressure thereof and returning the pressurized working fluid to said means for generating high temperature, high pressure working fluid, the improved combination in which the means for generating high temperature, high pressure working fluid comprises: a. at least one pair of spaced apart burner structures, the wall of each of said burner structures being made of sintered porous metal the voids of which have an effective pore size smaller than about 0.5 mm, b. first means embedded in the wall of the first burner structure for circulating fluid therethrough, c. second means embedded in the wall of the second burner structure for circulating fluid therethrough, d. a first cooler unit located in juxtaposition to and spaced from a surface of said first burner structure being disposed on the opposite side of said first burner structure from said second burner structure, said first cooler unit being adapted for the circulation of fluid therethrough, e. third means in flow communication with said first and second means for admitting fluid thereto, f. fourth means in flow communication with said first and second means for receiving fluid therefrom and with said first cooler unit for conducting fluId thereto, g. a second cooler unit located in juxtaposition to and spaced from a surface of said second burner structure being disposed on the opposite side of said second burner structure from said first burner structure, said second cooler unit being adapted for the circulation of fluid therethrough, h. fifth means in flow communication with said first cooler unit to receive fluid therefrom and with said second cooler unit for conducting fluid thereto, i. closure means affixed to the walls of each of said pair of burner structures, said closure means together with the walls affixed thereto defining a closed volume, j. means in flow communication with said closed volume for supplying a flow of fuel/air mixture thereto, k. means in communication with the space between said first burner structure and said first cooler unit for igniting fuel/air mixture released thereto through the wall of said first burner structure and l. means in communication with the space between said second burner structure and said second cooler unit for igniting fuel/air mixture released thereto through the wall of said second burner structure whereby non-adiabatic flame combustion can be conducted in said unit so as to insure low NOx concentrations in the burned gases.
 7. The improved Rankine-cycle power plant of claim 6 wherein the closed volume between the burner structures is subdivided into compartments and control means are provided for the fuel/air mixture supplying means for admission of the fuel/air mixture to each compartment.
 8. The improved Rankine-cycle power plant of claim 6 wherein the burner structures are in the form of hollow nested cylinders.
 9. The improved Rankine-cycle power plant of claim 8 wherein the first and second cooler units are hollow sintered porous metal cylinders, each cylinder having means embedded in the wall thereof for the circulation of fluid therethrough.
 10. The improved Rankine-cycle power plant of claim 6 wherein the closed volume between the burner structures is subdivided into compartments and control means are provided for the fuel/air mixture supplying means for admission of the fuel/air mixture to each compartment. 